Does Mirtazapine Cause Shortness of Breath?
Yes, mirtazapine can cause shortness of breath (dyspnea), though it is uncommon, occurring in approximately 1% of patients in clinical trials. 1
Evidence from FDA Drug Labeling
The FDA-approved drug label explicitly lists dyspnea (shortness of breath) as an adverse reaction that occurred in 1% of mirtazapine-treated patients compared to 0% in placebo-treated patients during 6-week controlled trials. 1 This represents a clear signal that mirtazapine can cause this symptom, even if infrequently.
Clinical Context and Mechanism
The occurrence of dyspnea with mirtazapine is particularly noteworthy given recent research attempting to use this medication to treat chronic breathlessness. A large 2024 phase 3 trial (BETTER-B) involving 225 patients with COPD or interstitial lung disease found that mirtazapine at doses of 15-45 mg daily over 56 days did not improve severe breathlessness and was associated with significantly more adverse reactions (64% in mirtazapine group vs 40% in placebo group). 2 This trial definitively concluded that mirtazapine should not be recommended as a treatment for severe breathlessness.
Common Side Effects to Monitor
The most common adverse reactions with mirtazapine include:
- Somnolence (54%)
- Increased appetite (17%)
- Weight gain (12%)
- Dizziness (7%)
- Dyspnea/shortness of breath (1%) 1
Serious Respiratory Considerations
Beyond simple dyspnea, the FDA label warns of potentially serious complications including:
- Serotonin syndrome - which can present with respiratory symptoms and respiratory arrest in severe cases 1
- Severe skin reactions that may involve lung organ involvement 1
Clinical Recommendation
If a patient develops new-onset shortness of breath after starting mirtazapine, consider it a potential adverse effect of the medication. Evaluate for other causes, but recognize this is a documented side effect. The risk-benefit analysis should be reassessed, particularly given that respiratory symptoms occurred more frequently than placebo in controlled trials. 1
The evidence does not support continuing mirtazapine if breathlessness is a concern, as the medication provides no benefit for this symptom and may potentially worsen it in susceptible individuals. 2